The pair, of Thessaly Road, Battersea, had denied their guilt after the robbery at a Co-operative store in Tattenham Corner on January 30 last year.

However jurors disagreed after an eight-day trial when they were told that events on the day started with a cream-coloured Chevrolet Captiva circling the shops in the area three times, apparently waiting for the cash delivery to be made.

'Pistol whip'

At 10.31am the security guard, former serviceman James Smith, found himself confronted by a man in a balaclava, the court heard.

Although it did not fire the weapon was then used to beat, or 'pistol whip' the victim, his helmet filling up with blood as he was struck on the upper chest and face, while fragments of his teeth were seen on his clothing, jurors heard.

The court was told Mr Smith suffered significant injuries to his face and hands, lost his front teeth and required bone grafts, implants and other ongoing dental treatment.

On being taken to hospital his wedding ring was removed due to swelling and he has been unable to wear it since.

Prosecutor Ian Hope said at the sentencing: "James Smith was beaten by the butt of the gun. He suffered psychologically. "He is determined to get on with the rest of his life but he is still affected by what happened and the events will stay with him for the rest of his life."

Designer shops

The offenders made off with £45,000 in £20 notes, the court heard, and though Terrance was arrested within hours of the offence, in his son's case it was six days later.

He was seen spending cash, mainly £20 in notes, in designer shops in the weeks after the robbery, witnesses at the trial said, and Terrance had planned home improvements including a new kitchen.

But Lewis claimed he was spending money made from amateur boxing and dealing cannabis, and the pair's barrister, Ben Hargreaves, said the money had been covered in purple dye so it was burnt, and the box containing it smashed up, on Box Hill.

It was accepted that Lewis was the gunman in this case but his father too has a history of firearms offences, the court was told.

'More able to cope in prison'

Terrance has 32 previous offences on his record, including a burglary in the late 1970s, an aggravated burglary at a jewellers a decade later during which a weapon was found following a rooftop chase, and two further firearms offences, the latter of which resulted in a jail term of 10-and-a-half years. He was released after that in 2011, the court heard.

Lewis has nine offences on his record, including a similar cash-in-transit robbery in 2005 for which he spent three years in a young offenders' institution.

Mr Hargreaves added: "It's accepted this was a sophisticated, planned, pre-meditated and serious assault done in an attempt to steal money."

Of Terrance Clark, the barrister said he had lived a life littered with serious offences but felt more able to cope with life in prison where he "knows what is going to happen day after day."

"He realises all his decisions have caused havoc in his family unit. His inability to live outside caused this offence."

Speaking of Lewis, Mr Hargreaves said the gun he had was a plastic 'BB' gun, and said he had only planned to use it to threaten, rather than beat anyone.

"Maybe he was trying to live up to his father's reputation," Mr Hargreaves added.

'Sheer greed'

In sentencing, Judge Robert Fraser told the duo that security guards like Mr Smith were "extremely vulnerable to people like you."

"It's very clear the impact on him," Judge Fraser said.

The judge jailed Terrance Clark to life imprisonment for the conspiracy to rob and a concurrent eight years for the firearms offence. He must serve a minimum of eight years and 138 days before being eligible for parole.

Lewis Clark was sentenced to 16 years for robbery and eight years concurrent for the firearms matter.

A Surrey Police investigation included what is believed to be the world's first reconstruction of a crime on Twitter, and this led to information being passed on to officers.

Senior Investigating Officer Detective Chief Inspector Paul Rymarz, said on Friday: "The sentence passed today demonstrates how dangerous and violent these individuals are and I am pleased they are now off the streets of Surrey for a long time.”

And Jaswant Narwal, Crown Prosecution Service South East chief crown prosecutor, added: "This was an appalling crime with the victim left with serious injuries following the robbery.

"The evidence showed that the defendants carefully planned this raid, with the motive appearing to be sheer greed."

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She has been editorial director of the online and print titles in Surrey and north-east Hampshire since 2007. Marnie previously worked at the BBC as a producer for 5 Live, having moved to national radio from BBC Sussex and Surrey.